Process and apparatus for the production of improved steel tubing



2 Sheets-Sheet 1 C4l40 steal Dec. 29, 1964 E. s. NACHTMAN PROCESS AND APPARATUS FOR THE PRODUCTION OF IMPROVED STEEL TUBING Filed Dec. 7, 1960 0'45 1'30 Beating Angle F: G. 5

INVENTOR. Elliot 3. Nachcm n m e no. A .wm mm M l m. /o o M. w a c 0; w 6 65 W mus-m m m M 2 2 I 1: .1. 5 .1 0 49 mm m .mw m w mumw mm w m 0 ll 0 U 00 TM m IL 0 w w m w w 0 0 0 5 Z I. +50 (at 2: 55; 23.2 33. 333

Dec. 29, 1964 s. NACHTMAN PROCESS AND APPARATUS FOR THE PRODUCTION OF IMPROVED STEEL TUBING 2 Sheets-Sheet 2 Filed Dec. 7, 1960 -56 wmi 636M @535? s 1 m 2 w 2 m a m r u 6 mm m m w m M w M w m V 4m n s a a m H. m 5 G a .1 1 5 u I. 4 a fid m 0 H 3 m .m I. e e 3 8 a 2 r F C C 2 M e w 8 w MM. r 3 5 0 M B 4 e 0 0 I C m D- 0 0 0 0 O 0 0 0 m w m w w m w 1 H -23 SL6 9.1 -50 $1 023. m mu u D D .m 5 h M uh 5 a 1m, w W 1. mm a I 0 q! I F m M m m o n a L) O H 0 O M m w 0 m w m a .m 3 1 I o was $2633. mc ud u FIG, 7

INVENTOR. Elliot .5, Nachtman I Cltt'ys United States Patent 3,163,285 PRGCESS AND APPARATUS FOR TEE PRODUC- TION 0F IMPROVED STEEL TUBING Elliot S. Nachtrnan, Oak Park, Ill., assi@or to La Salle Steel Company, Hammond, Ind, a corporation of Delaware Filed Dec. 7, 1960, Ser. No. 74,314 1 Claim. (Cl. 205-8) This invention relates to the production of steel tubing, and it relates more particularly to a process and apparatus for the elimination of residual stresses in steel tubing. In addition, this invention relates to a system which permits the introduction in a controlled manner of desirable stress patterns in steel tubing, thereby improving the mechanical properties of the tubing.

In the production of steel tubing, it is often necessary to work the tubing to obtain desirable size and to achieve certain degrees of strength and hardness. It is known that in the working of steel tubing, as by drawing, stresses of considerable magnitude may be introduced, depending upon the amount of draft and chemistry of the steel. The presence of residual stresses in steel products has an important influence in processing the steel into the finished product, and the residual stresses existing also have considerable influence on. the specification of .certain materials for particular uses and applications. Cracking of the tubing might occur immediately as the work leaves the working apparatus, during subsequent processing into a finished product, in finished stock storage, or in final u practical standpoint, unnecessarily increases the cost of v materials by reason of the scrap rate involved.

It is therefore an object of the present invention to produce steel tubing without substantial residual stresses or with a controlled stress pattern, such that improved mechanical properties result.

It is an additional object of this invention to produce steel tubing on a dependable basis, free of detrimental stresses, and without expensive stress-relieving operations.

It is a further object of this invention to provide a method for enabling the elimination of cracking after the tubing leaves the working apparatus, during subsequent processing, in storage, or in final assemblage of the tubing into a steel unit.

These and other objects of this invention will appear more readily when considering the disclosure and claims and when considering the accompanying figures, in which- FIGURE 1 is a cross-section of a typical die employed in the inventive tubing system;

FIGURES 2 and 3 graphically illustrate the effect of bearing angle of the die on the warping and cracking values of the worked tubing;

FIGURES 4 and 5 graphically illustrate the effect of I ice FIGURES 6 and 7 graphically illustrate the effect of bearing angle on the warping and cracking values when a mandrel is employed in conjunction with the die.

The present invention broadly relates to the working of steel tubes either by sinking of the tubing or when plug mandrels are employed. The invention relates more particularly to novel tube-drawing dies having tapered bearings, to mandrels having tapered surfaces, and to processes employing these dies and mandrels in various novel combinations; The combinations employed include the use of separate dies wherein individual drawing stages are employed with each die, or in the use of tandem dies wherein a single drawing stage is employed with the dies.

The use of the novel dies and the various arrangements thereof reduces the warping and cracking values of the tubing produced. These warping and cracking values are indications of the residual stress in the tubing, which stresses will ultimately control the ability of the tubing to perform satisfactorily under adverse loading conditions.

In order that the residual stresses could be measured, warping and cracking tests were employed. The Warping test is one designed to show the tendency of a tube' to distort because of residual longitudinal stresses. The test consists of cutting a diametral slot in the specimen to a prescribed length, usually four times the diameter. The diameter is measured before and after cutting, and the change in diameter is denoted as flare. Positive and negative flare values are used in the conventional sense as representing tensile and compressive surface stresses, respectively. The following formula is used to compute the warping value:

X diameter flare I Warpng value, percent (slot g y This test is easily made and quite inexpensive, but it gives only a gross approximation of the warping tendency due to the longitudinal stress. It is qualitative rather than quantitative because the wall thickness should be taken into account in comparing different tubes.

For an estimate of the longitudinal stress, the tongue test was used. This test is performed by'rnaking two parallel slots in the long direction of the tubing. The iso lated tongue will deflect to indicate the magnitude of the longitudinal stress. To get the maximum deflection, the width of the tongue should be 0.10 to 0.20 times the diam eter of the tubing. For the I -inch tubing tested in this program, the tongue width was to inch, and the length was four diameters, as it was for the warping test. The formula for calculation of the longitudinal stress is as follows: 7

Estimated longitudinal stress, p.s.i.=

modulus X Wall thickness flare (slot length) This formula is based on the assumption that the stress has an approximately linear distribution and is equal in magnitude but opposite in sign at the inside' and outside surfaces.

While the drawing of a tube through a die by sinking usually produces longitudinal stresses that may be un- Cracking value, per cent 100x flare circumference An estimated tangential stress may also be calculated by using the flare obtained in following formula:

Estimated tangential Stress, p.s.i.=

Modulus X Wall thickness H are 71' X (diameter) 2 The formula assumes that the tangential stress is linear. 35 a Th6 tubular the cracking test and'the 4. TABLE I Dimensions of Experimental Dies and M andrels Entrance Exit Length, Die Half Angle Dialn, Diam., inch inches inches Mandrel Taper- Exit Entrance Length,

N 0. Half Angle Side Diam Side Diam., inches inch inch B The blend angle for these dies is approximately 4, the approach angetgsgg to 12, and the entrance angle which is used for the large tubing Not actually measured, but slightly greater than 3 inches.

A specific phase of this invention consists in the drawing of steel tubes by a sinking operation, that is, drawing the tubes without the use of a mandrel. In order to illustrate the advantageous results which may be achieved with the novel process and apparatus of this invention, 15 steel tubes were drawn employing single dies. The drawing conditions and results are shown in Table II. The composition of the specimens was as follows:

. Percent The specific dies and mandrels employed to illustrate C 0A0 the inventive concepts are set forth in Table I, and refer,- Mn Q83 ence may be made to FIGURE 1 for an explanation of P 0 2 the terms employed. Symbols assigned to dies and tools 5 1014 in the following tables are purely arbitrary characters Si 0,25

employed for purposes of identification in the testing pro- Cr 0.75

cedures. Mo" 0.20

. TABLE II Tubes Drawn by Using a Single Die Without a Mandrel Reduction Distortion Tests B caring Tube Warping Tongue Cracking Tube Die Angle Diam.,

-, mches Diam., Area,

Percent Percent Flare, Value, Flare, Longitudi- Flare, Value, Tangential inch Percent inch 1131 Stress, inch Percent tress, p.s.i. p.s.i.

04140 STEEL TUBES 1 30 exhibit substantial decreases in longitudinal stress and tangential stress when compared to the specimens drawn through dies with zero bearing angles. FIGURES 2 and 3 graphically illustrate the improvements that are achieved, these figures being based on average values taken from Table II and on nominal percent reductions.

Table 111 illustrates the results that may be achieved using tandem dies or employing separate dies. use of the tandem dies, the successive reductions in the tubing are achieved by a single draw, whereas in the use of separate dies two separate draws were employed.

In the 6 hibited in the specimens 31 and,39, thus illustrating the value of tandem dies. Specimens 31 show superior properties relative to specimens 39 illustrating the value of the bearing angle even where separate dies are employed. Similar comparisons are available when considering specimens 43, 44 and 45 relative to specimens 41.

Reference to Table IV indicates substantial improvement in the warping and cracking values even without the tapers, although the tapers are shown to further improve the residual stress concentrations. It is noted that in the case of tube 38, reductions as low as 0.2% in the second stage improve the residual stress amounts, and tests indi cate that reductions greater than about 3% in the second stage will not significantly improve this property. The value of the second stage reduction is independent of the amount of the first stage reduction, and reductions in the TABLE III Tubes drawn by Using Tandem Dies or Two Dies Separately Distortion Tests First Die Second Die Reduction Tube Warping Tongue Cracking Tube Diam.,

inches Longi- Tangem. Bearing Bearing Dram., Area, Flare, Value, Flare, tudinal Flare, Value, tial No. Angle No. Angle Percent Percent inch Percent inch Stress, inch Percent Stress,

p.s.1. p.s.1.

TWO DIES SE1.

' 31A A250 045 1. 501 28. 9 33:6 +0. 070 +20, 900 +0. 0203 +0. 61 +33, 7 31B A340 0 1. 067 0.094 0. 98 +0. 025 +0. 148 +0. 104 +31, 000 +0. 0096 +0. 29 +15, 700 39A- A340 0 1. 502 30. 2 34. 6 +0. 043 +0. 250 +0. 2125 +63, 900 +0, 0500 +1. 52 +86, 500 3913. X1916 0 1. 047 0. 96 0. 18 +0. 065 +0. 371 +0. 215 +64, 800 0. 0188 +0.58 +33, 300 41A A250 045 1. 250 14. 6 l4. 9 +0. 010 +0. 059 +0. 2155 +45, 100 +0. 0281 +0. 84 +32, 000 4113 i A250 045 1. 068 0. 1 0. 7 +0. 005 +0. 027 +0. 107 +22, 600 +0. 0201 +0. +23, 400

TANDEM: DIES X1910 0 1. 502 31. 1 36. 9 +0. 022 +0. 120 +0. 001 +18, 000 +0. 0192 +0. 59 +33, 500 A340 0 1. 502 29. 0 34. 6 +0. 017 +0. 101 +0. 0775 +23, 000 +0. 0156 +0. 47 +25, 800 A340 0 1. 251 14. 8 17. 7 +0. 016 +0. 092 +0. 085 +17, 600 +0. 0272 +0. 81 +30, A250 045 1. 252 14. 8 16. 3 0. 008 0. 047 +0. 281 +41, 300 +0. 0353 +1. 05 +40, 600 A341 130 1. 250 14. 8 15. 5 -0. 005 -0. 030 +0. 098 +20, +0. 0221 +0. 60 +25, 600

The steel composition of the specimens was the same as that employed above. An analysis of the results reveals that no substantial difference in properties results 7 and tangential stresses, which improvements are due to the light reduction taken in the final Working operation.

It is additionally revealed that these same properties are improved over and above the improvement achieved by the light reduction when tapered dies are employed. The improvement in the amounts of longitudinal and tangential stresses in the warping and/ or cracking values is achieved whether the first, second, or both of the dies are tapered. The tests amplify the value of the tapers, in addition to showing the advantageous results that can be achieved when employing a second light reduction on the drawn products.

In considering the specific results shown in Table III, it will be noted that a reduction in longitudinal stress and tangential stress is effected in specimens 35 and 38 when these specimens are compared with the stresses ex I neighborhood of from 10% to about 50% reduction in area are contemplated in this phase of the invention.

With reference to the specific values in Table IV, it will be noted that the use of positive bearing angles provides superior results for tlnn wall tubes as seen in considering the values in the first grouping. Under the heading Dies in Tandem, the values illustrate the improvements that can be achieved with this arrangement. Under the heading Drawn in Separate Stages, the use of two. dies, each having a positive bearing angle, is indicated to be preferable to the use of a single die. 7

The heavy wall tubes also exhibit clear improvements as illustrated by the first group of samples wherein the sample 31A drawn through a die having a positive bearing angle is shown to have properties superior to the other samples. Under the heading Dies in Tandem, the use of a positive bearing angle provides improvements when comparing specimen 38 with specimen 35. Again, where the specimens 39B and 3113 were drawn in separate stages, the positive bearing angle again illustrates the point that improved properties can be achieved where this angle is employed.

TABLE IV First Die Second Die Distortion Values Tube N 0. Angle Reduction, N0. Angle Reduction, Warping, Cracking,

percent percent percent percent THIN-WALL TUBES 42 L18 00 +0. 167 +2.13 2, 28 A340 00 +0. 206 +2.13 1, 26, 29, 30 A250 045 +0. 107 .+0. 87 3 A341 130 +0.100 +1.20

DIES IN TANDEM 00 14.8 A340 00 2. 9 +0. 092 +0. 81 00 14. 8 A250 045 1. 5 0. 047 +1. 05 00 14.8 A341 130 0. 7 0. 030 +0. 66

DRAWN'IN SEPARATE STAGES 41A A250 045 14.9 +0059 +0.84 41B A250 045 14.9 A250 045 0.7 +0027 +0.60

DIES IN TANDEM A340 00 35. 7 X1916 00 1. 2 +0. 126 +0. 59 A250 045 34. 4 A340 00 0.2 +0. 101 +0. 47

' DRAWN IN SEPARATE STAGES 39B A340 00 34.6 X1916 00 0.18 +0. 371 +0.58 31B A250 045 33.6 A340 00 0.98 +0. 148 +0.29

8 Nominal dimensions were IM-inch 0D x %-iuch wall. b Nominal dimensions were 1%-inch OD x eta-inch wall.

FIGURES 4 and 5 are made up from average values compiled from the data in Table III. These figures illustnate the improvement which is obtained in the cracking 45 and warping values when a slight bearing angle is employed in the die, and also illustrate the advantage of the double draw as opposed to the use of a single die.

The data shown in Table V illustrates the. results that are obtained when drawing tubing while employing a plug mandrel. The use of a mandrel is ordinarily resorted to Where it is desired to control thewalllthickness of the drawn product and/ or the inner diameter of the product. The specimens used in this portion of the work had the same composition as that noted above.

. TABLE V Tubes Drawn by Using a Mandrel Distortion tests Mandrel Reduction Tube Warping Tongue Tube Die Bearin Diam., angle inches Longitu- Diam., Shape Diam., Area, Flare, Value, Flare, dinal inch percent percent inch percent inch Stress,

' C4140 STEEL TUBES 0 1. 250 14. 9 22. 3 0. 0005 0. 003 +0. 042 +8, 000 +0. 0063 +0. 19 0 1.249 14. 7 20. 7 0. 003 0. 018 O. 027 6, 100 +0. 0029 +0.09 0 1. 251 14. 9 19. 0 -0. 003 --0. 018 +0. 078 +15, 500 +0. 0162 +0. 49 0 1, M9 14.8 17.0 +0. 004 +0. 024 +0. 119 +23, 800 +0. 0188 +0. 56 0 1. 250 14. 9 18. 9 +0. 026 +0. 153 +0. 347 +69, 700 +0. 0583 +1. 75 0 1. 249 14. 8 15. 2 +0. 022 +0. 127 +0. 307 +62, 70 +0. 0462 +1. 38 0 1. 501 29. l 39. 2 +0. 001 +0. 006 +0. 018 +4. 800 +0. 0060 +0. 18 0 1. 250 14.6 18. 6 +0. 013 0. 077 O. 112 -21, 800 +0. 0134 +0.40 0 1. 250 14.3 16. 7 0. 012 0. 071 O. 043 8. 500 +0. 0151 +0. 45 0 1. 250 14. 7 17. 5 0. 014 0. 083 0. 133 26, 500 +0. 0087 045 1, 250 14. 7 18.9 0. 006 0. 036 0. 068 13, 000 045 1, 250 14. 8 19. 9 0. 014 0. 080 0. 101 +19, 800 045 1. 250 14. 7 18. 2 O. 005 O. 030 0. 08 13, 000 036 1. 501 29. 2 40. 0 +0. 0018 130 1. 248 14. 7 20. 1 0. 006 0. 036 -0. 098 18, 500

I Mandrel was allowed to slip past the end of the bearing of the die 1/2 inch.

b Mandi-e1 was positioned in the die so that the maximum diameter was adjacent to the exit end of the bearing section of the die.

It will be seen, when studying this data, that the use of a mandrel significantly reduces the residual stress. It is significant to note that when tapers are employed in the die and/or in the mandrel, significant amounts of compressive stresses (indicated by the negative sign) are produced, and that with a tapered die and a cylindrical mandrel, compressive stresses are introduced at the inside and at the outside of the tube. It is well known that compressive stresses will improve the fatigue life of metals, improve their general corrosion resistance, and also improve the resistance to stress corrosion cracking.

With reference to the specific values shown in Table V, it will be noted when comparing specimens 20, 50, 49, 57, 54 and 58 with specimens 15, 51, 23 and 19 that distinct improvements in the longitudinal and tangential stress are available when employing a positive bearing angle. When comparing specimens 21 and 24, similar improvements in the tangential stress are also to be noted.

FIGURES 6 and 7 iilustrate the effect of the bearing angle on the warping and cracking values where cylindrical mandrels are employed, and the figures also compare residual stress with percent reduction obtained by a man drel draw as opposed to the residual stresses occurring after sinking.

The dies and mandrels of the foregoing examples having the disclosed tapers are particularly suitable for the improvement in amounts of residual stresses and for the introduction of desirable stress patterns. However, tests have indicated that variations in bearing angle taper in the dies may be from about 30 to about 2 and still provide satisfactory results, While tapers up to about 1 will give the best results insofar as mandrel tapers are concerned.

It is contemplated that the inst-ant process will be applicable to carbon and alloy steels generally of varying tubular cross-sections, and of any well-known diameter. Although the invention has been described with reference to cold drawing, processes of tube drawing under other conditions are contemplated, for example, processes which include drawing of steel at temperatures between about 100 F. and the lower critical.

It will further be understood that the die and mandrel tapers of this invention are peculiarly adaptable to other well known tube producing processes, particularly extrusion. Extruded tubing, having been forced through dies comprising the inventive concepts heretofore set forth likewise exhibits improved mechanical characteristics over tubing produced in conventional extrusion type. This is particularly true with regard to warping and cracking.

values. A tube so extruded may be then drawn through a second die in the manner heretofore set forth in order to achieve the advantages of this concept of the invention. EXtrud-ing conditions, including ram pressure, temperatures, etc. are conventional.

It will be understood that the foregoing process and apparatus has been described with reference to specific examples and that changes may be made therein without departing from the scope of this invention, especially as defined in the following claims.

I claim:

In a method of drawing tubular products wherein a mandrel is operatively associated with a die to effect reduction in the wall thickness of the tubes being drawn, the improvement comprising providing a die member having an inlet and an outlet portion and a bearing portion, the inner diameter of said die member at said bearing portion decreasing progressively toward said outlet portion in a manner such that a line intersecting the axis of said die and lying parallel to the inner surface of said bearing portion forms an angle within the range of 0 to 1 30', and advancing the tubular product through said die to effect reduction in the cross sectional area during passage through the bearing.

References Cited in the file of this patent UNITED STATES PATENTS 2,237,112 Parvin Apr. 1, 1941 2,250,610 Simons July 29, 1941 2,270,398 Westin Jan. 20, 1942 2,589,881 Sims Mar. 18, 1952 2,721,651 Roth Oct. 25, 1955 FOREIGN PATENTS 423,868 Great Britain Feb. 11, 1935 56,974 Holland Sept. 15, 1944 OTHER REFERENCES Brochure of Vascoloy Ramet Corporation, North Chicago, Illinois, April 1941. 

